Apparatus and method for retarding an engine with an exhaust brake and a compression release brake

ABSTRACT

An apparatus and method for retarding an engine having a cylinder with an exhaust valve, an intake valve, an intake stroke, an exhaust stroke, a compression stroke and an expansion stroke. The apparatus includes an exhaust brake and a compression release brake. The exhaust brake includes a variable exhaust restrictor, a pressure sensor for sensing pressure of exhaust gases and a controller operatively connected to the pressure sensor and to the exhaust restrictor. Opening of the exhaust restrictor is adjusted during operation of the apparatus so exhaust pressure is sufficient to cause exhaust valve float prior to bottom dead center of intake strokes of the cylinder, thereby enhancing operation of the compression release brake.

BACKGROUND OF THE INVENTION

This invention relates to methods and apparatuses for retarding enginesand, in particular, to compression release brakes, such as bleederbrakes, and to exhaust brakes.

Conventional compression release brakes retard engines by opening theexhaust valves just prior to Top Dead Center (TDC) of the compressionstroke. This creates a blow-down of the compressed cylinder gas and theenergy used for compression is not reclaimed. The result is enginebraling, or retarding, power. This type of brake has substantial costassociated with the hardware required to open the exhaust valves againstthe extremely high load of the compressed cylinder charge. The valvetrain components must be designed and manufactured to operate reliablyat high mechanical loading. Also, the sudden release of the highlycompressed gas causes high noise levels. This means that engine brakescannot be used in certain areas, typically urban areas, leading to apotential safety hazard.

The power generated by an engine brake is directly proportional to themass of air that is charged into the cylinder before compression. On aconventional system, the turbocharger compressor provides this air. Itis beneficial, therefore, to keep the turbocharger speed as high aspossible to maximize cylinder charge. Braking power may fall off sharplyat reduced engine speeds, when the turbocharger slows down and deliversless air to the cylinder.

Exhaust brakes can be used on engines where compression release loadingis too great for the valve train. The exhaust brake mechanismconventionally consists of a restrictor element mounted in the exhaustsystem. When this restrictor is closed, back pressure resists the exitof gases during the exhaust cycle and provides a braking function. Thesystem provides less braking power than a compression release brake, butis also less costly. As with a compression release brake, the retardingpower of an exhaust brake falls off sharply as engine speed decreases.This happens because the restriction is normally optimized to generatemaximum allowable back pressure at rated engine speed. The restrictionis simply insufficient to be effective at lower engine speeds.

U.S. Pat. No. 5,086,738 to Meneely discloses a system to enhance enginebraking power by combining an exhaust brake with a compression releasebrake. With both brakes on, a high-pressure pulse from an adjacentcylinder in the same exhaust manifold superimposes on the raised averageexhaust pressure. Enough force is generated to temporarily open theexhaust valves against the exhaust valve spring preload. This opening byovercoming the valve springs is referred to as “valve float”. Thisoccurs naturally around the end of the intake stroke. The high-pressuregas in the exhaust manifold supercharges the cylinder through the openexhaust valve just before the brake event. Compression begins at ahigher cylinder pressure and is compressed to a higher peak value forthe blow-down. In addition, an exhaust brake component is provided byvirtue of the high exhaust pressure with the operation of the exhaustbrake. This approach is mainly effective only at high engine speeds asthe conditions for valve float diminish quickly as engine speeddecreases.

U.S. Pat. No. 6,170,474 to Israel discloses a method for exhaustpressure regulation by controlling an internal exhaust gas recirculationprocess. The control is carried out responsive to monitored levels ofexhaust pressure and/or temperature. A restriction is provided in theexhaust system to raise exhaust pressure. A reopening of the engineexhaust valves is introduced to provide a passage for exhaust gas tore-enter the cylinder from the exhaust manifold. This simultaneouslyrelieves exhaust system pressure and supercharges the cylinder forengine braking. By controlling the timing and magnitude of this event,exhaust pressure is regulated.

Retarding power on the order of the rated power of the engine can beachieved by combining a bleeder brake with an exhaust brake. U.S. Pat.No. 5,215,054 to Meneely incorporates a catch mechanism that holds theexhaust valve open at the end of the exhaust stroke, at the levelrequired to bleed the cylinder during the compression stroke.

Further gains in retarding power can be attained with a combination of ableeder-exhaust brake by raising the exhaust pressure to where naturalvalve float occurs. U.S. Pat. No. 5,787,858 to Meneely uses thistechnique to supercharge the cylinder prior to the compression stroke.The valve is reseated near the end of the compression stroke by means ofelectronic triggering of a solenoid valve.

A Microprocessor Controlled Exhaust Brake is disclosed in PCTPublication No. WO 02/086300 to Anderson et al. Here the opening of theexhaust brake is regulated according to the exhaust pressure and, insome embodiments, according to the exhaust temperature. A controller,acting through a solenoid, adjusts the exhaust brake, typically abutterfly valve.

Despite these earlier devices, however, there still remains asignificant need for a low-cost engine braking system that can beintegrated into an overall engine design. A practical system shouldprovide sufficient retarding power without overloading the mechanicaland thermal components of the engine. It should provide mass charging tothe cylinders from the intake and exhaust subsystems prior to thecompression and release events that is sufficient to generate optimumretarding power at all engine speeds. It should also provide quietoperation so as to be useful in environments sensitive to noisepollution. Therefore, a means of regulating exhaust pressure must alsobe provided.

SUMMARY OF THE INVENTION

According to one aspect of the invention, an apparatus for retarding anengine has a cylinder with an exhaust valve, an intake valve, an intakestroke, an exhaust stroke, a compression stroke and an expansion stroke.The apparatus includes an exhaust brake and a compression release brake.The exhaust brake includes a variable exhaust restrictor, a pressuresensor for sensing pressure of exhaust gases, a controller operativelyconnected to the pressure sensor and to the exhaust restrictor so as toadjust opening of the exhaust restrictor during operation of theapparatus so exhaust pressure is sufficient to cause exhaust valve floatprior to bottom dead center of intake strokes of the cylinder, therebyenhancing operation of the compression release brake.

According to another aspect of the invention, there is a method forretarding an engine apparatus having a cylinder with an exhaust valve,an intake valve, an intake stroke, an exhaust stroke, a compressionstroke and an expansion stroke. The apparatus includes an exhaust brakeand a compression release brake. The exhaust brake includes a variableexhaust restrictor, a pressure sensor for sensing pressure of exhaustgases, a controller operatively connected to the pressure sensor and tothe exhaust restrictor. The controller adjusts opening of the exhaustrestrictor during operation of the apparatus so exhaust pressure issufficient to cause exhaust valve float prior to bottom dead center ofintake strokes of the cylinder, thereby enhancing operation of thecompression release brake.

The invention offers significant advantages over the prior art. Comparedto a conventional compression release brake, it does not require theexpensive hardware required to open exhaust valves against the extremelyhigh load of the compressed cylinder charge. However, at low enginespeeds engine braking is enhanced because the exhaust restrictor isclosed a sufficient amount to maintain a pressure which causes exhaustvalve float, and thereby enhances operation of the bleeder brake at lowengine speeds as well.

Moreover the invention provides a low-cost engine braking system whichcan be integrated into overall engine design. Mechanical and thermalcomponents of the engine are not overloaded since the exhaust restrictorcan be adjusted below maximum temperature and pressure limits.

Finally, by regulating exhaust pressure, the system ensures relativelyquiet brake operation compared with conventional compression releasebrakes. Thus engine braking systems according to the invention may beutilized in environment sensitive to noise pollution, such as urbanareas.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagrammatic view of an internal combustion engine equippedwith an engine retarding system according to an embodiment of theinvention;

FIG. 2 is a sectional view of the hydraulically extensible memberthereof;

FIG. 3 is a sectional view of the rocker arm, adjustment screw andhydraulically extensible member;

FIG. 4 is a valve lift profile diagram of the engine of FIG. 1 equippedwith the engine retarding system in the retarding mode; and

FIG. 5 is a Pressure-Volume diagram thereof showing the retarding powercomponents of the engine retarding system.

DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Referring to the drawings and first to FIG. 1, this shows an internalcombustion engine 10, a diesel engine in this instance, equipped with aplurality of cylinders, only cylinder 12 being shown for simplicity.Each cylinder is provided with a piston 14 which reciprocates therein.Each cylinder has an exhaust valve 16 and an intake valve 18. Eachcylinder may have more than one intake valve and/or exhaust valve, butagain only one of each is shown for simplicity. The engine also has anintake manifold 20 and an exhaust manifold 22.

In the conventional manner exhaust valve 16 is opened by rotation ofrocker arm 24 about rocker arm shaft 26 in the direction indicated byarrow 28. The rocker arm is provided with an adjustment screw 29 capableof adjusting clearance between the rocker arm and the valve.

The exhaust manifold 22 is connected to a turbocharger 34 by an exhaustconduit 36. The turbocharger includes a compressor 38 and a turbine 40.The exhaust gases exit the turbine through conduit 42, which comprisesexhaust brake 44. Air compressed by the compressor 38 is carried by aconduit 50 to the intake manifold 20 through charge cooler 52. In thisexample of the invention the exhaust brake is a MicroprocessorControlled Exhaust Brake as disclosed in PCT Publication No. WO02/086300 to Anderson et al., which is incorporated herein by reference,although other variable exhaust restrictions could be substituted. Forexample, a highly restrictive turbocharger may be employed. This may bea variable wastegate or a variable geometry type. Alternatively therestriction may be placed before or after the turbine. Where therestriction is installed upstream of the turbine, advantage is taken bygenerating a high-pressure differential across it.

In this example the exhaust restrictor is in the form of a butterflyvalve 54 in the exhaust conduit 42. The butterfly is rotated by linkage56 connected to an actuator 60, a pneumatic actuator in this particularexample, although other actuating devices could be substituted. Theactuator is actuated by a solenoid valve 62 which communicates with acontroller 64. The controller receives pressure and temperature signals66 and 68 from sensors 70.

Referring to FIGS. 2 and 3, the rocker arm 24 has a hydraulic extensionmember 71 including a lifter body 72 reciprocatingly mounted within acylindrical bore 74 and held in by a retainer ring 83. The lifter bodyhas a ball-like end 76 received in socket 78 of exhaust valve interfacemember 80 which contacts top 82 of the exhaust valve 16. There is aretaining ring 84 which holds the ball and socket assembly together.

The lifter body has an internal bore 86 which reciprocatingly receives aplunger 88. Radial clearance 89 is provided between the plunger and thebore. The plunger has a protrusion 90 which extends above the top 92 ofthe lifter body by an amount 94 when the plunger is in its uppermostposition has shown in FIG. 2. There is a retaining ring 96 within thebore which contacts shoulder 98 of the plunger to limit upward movementof the plunger from the point of view of FIG. 2. However protrusion 90is sized to fit through the retaining ring. A hydraulic chamber 91 islocated within the bore 86 below the plunger.

There is an internal passageway 100 extending longitudinally through theplunger including a relatively narrow hydraulic conduit 102 adjacent tothe top of the plunger, a wider portion 104 below portion 102 and astill wider portion 106 below portion 104. A check valve 110 is locatedwithin portions 104 and 106 including a ball 112 within the portion 104.A valve seat 114 for the check valve is formed between the portions 102and 104. The ball of the check valve is biased upwardly by a coil spring116 having its bottom within a recess 118 at the bottom of bore 86.

Another coil spring 120 is fitted between shoulder 122, where portions104 and 106 of passageway 100 meet, and the bottom of the bore. Thisspring biases the plunger upwardly from the point of view of FIG. 4.There is a collar 124 fitted between the springs 116 and 118 within theplunger and which contacts the shoulder 122.

As may be seen, the hydraulic conduit 102 extends through the top 126 ofthe plunger. A second hydraulic conduit 128 extends through the plungerand intersects the conduit 102 below the top.

During normal engine operation underpower, the exhaust restrictor 54 ofexhaust brake 44 shown in FIG. 1 remains open. However, when thethrottle is closed, and engine retarding or braking is desired, therestrictor is closed sufficiently by controller 64, acting throughsolenoid 62 and actuator 60, to cause valve float of the exhaust valve16 near the end of the intake stroke for cylinder 12. This valve floatis illustrated at 502 in FIG. 4. The degree by which the restrictor isclosed is determined by the processor to give sufficient pressure tocause the exhaust valve float. However this is done within designatedexhaust pressure and exhaust temperature limits as sensed by sensors 70to avoid excess strain or damage to the engine. The controller includesa lookup table of exhaust pressure values which are sufficient to causevalve float of the exhaust valves, but are below maximum pressurevalues.

The amount of exhaust valve gap or lash 136, shown in FIGS. 1 and 3,increases when the valve floats. The amount 94 of the plunger 88extending above the top 92 of the lifter body 72, as shown in FIG. 2, isgreater than the exhaust valve lash. When the valve floats, the plunger88 moves upwardly, from the point of view of FIG. 2, to its uppermostposition and hydraulic fluid, in this example engine oil, enters throughhydraulic conduit 102 and fills the chamber 91. When the exhaust valveattempts to close after floating, it is held opened by the interfacemember 80 on the bottom of lifter body 72 which has been extendeddownwardly to close gap 136 by the upward movement of plunger 88contacting adjustment screw 29.

The radial clearance 89 between the plunger and the bore 86 permitshydraulic fluid to gradually leak out of chamber 91 with continuedupward pressure of the exhaust valve. This permits the exhaust valve inthis example to effectively close just after the end of the compressionstroke as seen at 140 in FIG. 4. The valve may close from the bleederlift prior to the normal exhaust stroke, or the excess lift may bleedout of chamber 91 during opening of the normal exhaust event. Thecritical thing is that the exhaust valve be closed or nearly closed atthe end of the exhaust stroke. The valve may remain open some smallamount in the order of 0.005″-0.010″.

As seen in FIG. 4, the main exhaust event 500 and the main intake event600 occur at their normal times. When the pressure is raisedsufficiently in the exhaust manifold by closing the restrictor 54, theforce on the back of the exhaust valve 16 overcomes the resisting forceof the valve spring 17 seen in FIG. 1. Exhaust gases are then forcedinto the cylinder 12. This charges cylinder 12 prior to the compressionstroke. As the exhaust valve 16 moves away from the valve train, the gap136 shown in FIG. 3 is taken up by the upward movement of the plunger 88and consequent downward movement of lifter body 72. This holds theexhaust valve off its seat for the remainder of the compression strokeas seen at 150 and 152 in FIG. 4. As pressure in the cylinder builds,however, the exhaust valve moves back to its reseated position due tothe leakage of hydraulic fluid past radial clearance 89 as well as dueto compression of the hydraulic fluid within chamber 91. The valveclosing by oil compression is recovered as the forces subside, but valveclosing by leakage does not recover and lost fluid must be refilled oneach engine cycle.

During normal engine operation, under positive power, the restrictor 54is open and there is no valve float. The hydraulic link comprisinglifter body 72 and plunger 88 remains loaded throughout the engine cycleand cannot expand to hold the exhaust valve off its seat. The enginebrake is thus disabled.

The engine brake has two performance components. The bleeder brakecomponent comprises the holding open of the exhaust valve by thehydraulic link, or extension member 71 comprising lifter body 72 andplunger 88. This works during the compression stroke, the work beingillustrated at 800 in FIG. 5. The exhaust brake component, caused by theclosing of exhaust restrictor 54, works during the exhaust stroke and isshown at 900 in FIG. 5. The total retarding work is represented by thearea bounded by the two loops in the curve of the pressure-volumediagram.

It will be understood by someone skilled in the art than many of thedetails above are given by way of example only and can be altered ordeleted without departing from the scope of the invention as set out inthe following claims.

1. An apparatus for retarding an engine having a cylinder with anexhaust valve, an intake valve, an intake stroke, an exhaust stroke, acompression stroke and an expansion stroke, the apparatus including anexhaust brake and a compression release brake, the exhaust brakeincluding a variable exhaust restrictor, a pressure sensor for sensingpressure of exhaust gases, a controller operatively connected to thepressure sensor and to the exhaust restrictor so as to adjust opening ofthe exhaust restrictor during operation of the apparatus so exhaustpressure is sufficient to cause exhaust valve float prior to bottom deadcenter of intake strokes of the cylinder, thereby enhancing operation ofthe compression release brake.
 2. The apparatus of claim 1, wherein thecompression release brake is a bleeder brake and includes a device formaintaining the exhaust valve open during the compression stroke.
 3. Theapparatus of claim 2, wherein the engine has a valve opening mechanismfor the exhaust valve, said device for maintaining the exhaust valveopen including a hydraulic device.
 4. The apparatus of claim 3, whereinthe valve opening mechanism for the exhaust valve includes a rocker arm,the device for maintaining the exhaust valve open including ahydraulically extendable member mounted on the rocker arm which contactssaid exhaust valve.
 5. The apparatus of claim 4, wherein the member isreciprocatingly mounted in a cylinder on the rocker arm, a passagewayproviding hydraulic fluid to the cylinder to extend the member whenthere is clearance between the member and the valve.
 6. The apparatus ofclaim 5, including a check valve for inhibiting hydraulic fluid flowingfrom the cylinder to the passageway when the rocker arm moves towardsthe exhaust valve.
 7. The apparatus of claim 6 including meanspermitting controlled leakage of hydraulic fluid from the cylinderduring the compression stroke so as to allow the exhaust valve toeffectively close at completion of the exhaust stroke.
 8. The apparatusof claim 1, wherein the exhaust restrictor is a butterfly valve.
 9. Theapparatus of claim 1, wherein the exhaust restrictor is a variablyrestrictive turbocharger.
 10. The apparatus of claim 2, wherein thedevice maintains the exhaust valve open throughout the compressionstroke.
 11. The apparatus of claim 1, wherein the controller includes alookup table of exhaust pressure values which are sufficient to causesaid valve float of the exhaust valve, but below a maximum value. 12.The apparatus of claim 1, including a temperature sensor for sensingexhaust gas temperatures, the temperature sensor being operativelyconnected to the controller, the controller adjusting the exhaustrestrictor so the exhaust temperature remains below a maximum value. 13.A method for retarding an engine apparatus having a cylinder with anexhaust valve, an intake valve, an intake stroke, an exhaust stroke, acompression stroke and an expansion stroke, the apparatus including anexhaust brake and a compression release brake, the exhaust brakeincluding a variable exhaust restrictor, a pressure sensor for sensingpressure of exhaust gases and a controller operatively connected to thepressure sensor and to the exhaust restrictor, the method comprisingadjusting the opening of the exhaust restrictor during operation of theapparatus, utilizing the controller and exhaust restrictor, so exhaustpressure is sufficient to cause exhaust valve float prior to bottom deadcenter of intake strokes of the cylinder, thereby enhancing operation ofthe compression release brake.
 14. The method of claim 13, wherein thecompression release brake is a bleeder brake and maintains the exhaustvalve open during the compression stroke.
 15. The method of claim 14,wherein the engine has a valve opening mechanism for the exhaust valve,the exhaust valve being maintained open hydraulically.
 16. The method ofclaim 15, wherein the valve opening mechanism for the exhaust valveincludes a rocker arm, the exhaust valve being maintained opened by ahydraulically extendable member mounted on the rocker arm which contactssaid exhaust valve.
 17. The method of claim 16, wherein the member isreciprocatingly mounted in a cylinder on the rocker arm, hydraulic fluidbeing provided through a passageway to the cylinder and extending themember when there is clearance between the member and the valve.
 18. Themethod of claim 17, including a check valve which inhibits hydraulicfluid flowing from the cylinder to the passageway when the rocker armmoves towards the exhaust valve.
 19. The method of claim 18 includingthe step of permitting controlled leakage of hydraulic fluid from thecylinder during the compression stroke so as to allow the exhaust valveto effectively close at completion of the exhaust stroke.
 20. The methodof claim 13, wherein the exhaust is restricted by a butterfly valve. 21.The method of claim 13, wherein the exhaust is restricted by a variablyrestrictive turbocharger.
 22. The method of claim 14, wherein theexhaust valve is kept open throughout the compression stroke.
 23. Themethod of claim 14, wherein the controller utilizes a lookup table ofexhaust pressure values which are sufficient to cause said valve floatof the exhaust valve, but below a maximum value.
 24. The method of claim13, including a temperature sensor for sensing exhaust gas temperatures,the temperature sensor being operatively connected to the controller,the controller adjusting the exhaust restrictor so the exhausttemperature remains below a maximum value.